TechnitiumSoftware/DnsServer · error · ArgumentOutOfRangeException

Reserved address must be in scope range.

Error message

Reserved address must be in scope range.

What it means

Thrown by the ReservedLeases setter when a reserved lease's Address lies outside the scope's start..end range (IsAddressInRange returns false). Reservations must pin an address that belongs to the pool, so an out-of-range reservation is rejected.

Source

Thrown at DnsServerCore/Dhcp/Scope.cs:2179

                leases.Sort();
                return leases;
            }
            set
            {
                if ((value is null) || (value.Count == 0))
                {
                    //remove all DNS entries
                    foreach (KeyValuePair<ClientIdentifierOption, Lease> entry in _reservedLeases)
                        _dhcpServer.RemoveDnsEntries(this, entry.Value, true);

                    _reservedLeases.Clear();
                }
                else
                {
                    foreach (Lease reservedLease in value)
                    {
                        if (!IsAddressInRange(reservedLease.Address))
                            throw new ArgumentOutOfRangeException(nameof(ReservedLeases), "Reserved address must be in scope range.");
                    }

                    //remove DNS entries for reserved leases being removed or has updated domain name
                    foreach (KeyValuePair<ClientIdentifierOption, Lease> entry in _reservedLeases)
                    {
                        Lease existingReservedLease = entry.Value;
                        bool domainNameMatches = false;

                        foreach (Lease reservedLease in value)
                        {
                            if (existingReservedLease.ClientIdentifier.Equals(reservedLease.ClientIdentifier))
                            {
                                domainNameMatches = (existingReservedLease.HostName is null) || existingReservedLease.HostName.Equals(reservedLease.HostName, StringComparison.Ordinal);
                                break;
                            }
                        }

                        if (!domainNameMatches)

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Filter reservations so every Address lies within scope.StartingAddress..scope.EndingAddress.
2. After ChangeNetwork, migrate or drop reservations that fall outside the new range.
3. Validate reservation addresses in your config layer.
4. Do not reserve the network or broadcast address.

Example fix

// before
scope.ReservedLeases = reservations; // may contain out-of-range addresses

// after
var inRange = reservations
    .Where(r => IsInRange(r.Address, scope.StartingAddress, scope.EndingAddress))
    .ToList();
scope.ReservedLeases = inRange;

static bool IsInRange(IPAddress a, IPAddress lo, IPAddress hi)
    => Compare(a, lo) >= 0 && Compare(a, hi) <= 0;

reservations = reservations
    .Where(r => IsInRange(r.Address, scope.StartingAddress, scope.EndingAddress))
    .ToList();
scope.ReservedLeases = reservations;

static bool ReservationInRange(Lease r, IPAddress lo, IPAddress hi)
    => IsInRange(r.Address, lo, hi);

try { scope.ReservedLeases = value; }
catch (ArgumentOutOfRangeException ex) when (ex.ParamName == "ReservedLeases")
{ /* drop out-of-range reservations and retry */ }

When it happens

Trigger: Setting scope.ReservedLeases = collection where any reservedLease.Address is below the scope start or above the scope end. Common after ChangeNetwork moves the range without updating reservations.

Common situations: Migrating reservations between scopes, stale config after a network change, or reserving the broadcast/network address.

Related errors

• Ending address must be greater than starting address.
• Exclusion starting address must be in scope range.
• Exclusion ending address must be in scope range.
• The address must be an IPv4 address: {startingAddress}
• The address must be an IPv4 address: {endingAddress}

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/ccc0eca2d8dd3544. Report an issue: GitHub.